Laterite Regolith Gold Exploration

Due to the strong rise in gold price since 2021, gold projects in tropical laterite terrain are increasingly shaped by artisanal and small-scale gold mining (ASGM).

Tropical Laterite Regolith

Field examination of a classical tropical laterite regolith profile, displaying laterite and mottled zone horizons, while conducting a site visit of the Busetima gold mine in Uganda.

Regolith is everything that covers the bedrock, including vegetation, soil and loose rocks.

The tropical laterite regolith is quite deep, can be 4 to 8 meters thick, and in some places up to 100 meters or more before reaching fresh bedrock.

The deep laterite weathering is the result of warm climates, seasonal rainfall, and geological time.

Where it overlies gold-bearing rocks and veins, the laterite and saprolite are capable of hosting supergene gold enrichment.

Typical soil pit in tropical climates, showing dark brown coloured top soil (A) overlying red laterite B soil. The B soil is the geochemical soil sample of choice.

Soil Geochemistry Training

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Laterite B soil sampling is a precise discipline. Consistent, correct soil horizon identification is what turns raw soil into discovery data.

The laterite regolith starts with the O layer, which has vegetation and is organic.

Followed by the A top soil, which is dark-grey brown in colour and has many fine white rootlets growing in it.

Next is the red laterite soil, the B soil. It has a clay rich matrix and can be massive or gravelly.

Mynah Exploration has trained exploration and field teams in the Gold Exploration in Tropical Landscapes course, including best practices in soil geochemistry, in Canada, Jamaica, Nicaragua, The Philippines, Zambia and Gabon.

The course was also presented by Mynah Exploration on the GeoHug platform, follow this link.

Exposure of laterite regolith, on top the organic layer (vegetation), then the A-top soil in dark grey brown with the fine hairlike white plant rootlets, followed by the red laterite soil, which is the sample of choice in soil geochemistry surveys.

Soil Geochemistry Grid Design

Soil grids are best designed with soil lines perpendicular to the regional shear trend.

Soil lines can be spaced 200 to 400 meters apart.

Soil sampling stations are typically every 40 meters.

This design can define where the primary gold system daylights, and generates trench and drill-ready targets.

Exposing and mapping the saprolite by trenching the strong gold in soil anomalies can reveal which way the gold-bearing structures are dipping and support drill program design.

Gold results from laterite B soil geochemistry. The soil lines are perpendicular to the Dugbe shear trend and placed 250 meters apart. Soil sampling stations every 40 meters. The 2.4 million ounce gold deposits daylights at the soil anomaly.

On-Site Geological Training

On-Site Geoscience Course:

Course material is tailored to gold project site and covers:

Tropical laterite regolith. Gold dispersion within laterite soils. Formation of gold nuggets in the laterite regolith. Plate tectonics and paleoclimatic history of project area. Mineral exploration. Bre-X and what we have learned from it. Stream sediment sampling. Soil geochemical surveys. Trenching and drill targeting. Structural controls and geometry of orogenic, shear-zone (greenstone)-hosted gold deposits. Mineral alteration of orogenic gold deposits. (2 to 3 Days)

Diagram of gold dispersal in tropical laterite regolith, showing supergene gold enrichment, quartz veins, stockwork, shear zones, and different mineral zones such as saprolite, mottled zone, oxides, fresh rock, with labels and color-coded zones.

Practice: Field Component

Field Site: Laterite regolith exposures, pit and trenches, artisanal and small-scale gold mine sites, drill core review (if available). Soil geochemistry sampling protocols. (2-3 days)

Exploration team in course Gold Exploration in Tropical Landscapes with Mynah Exploration looking at a large laterite regolith exposure in a freshly excavated square pit.

Skills and Knowledge Transfer

“It is incredibly rewarding to see field geologists look at laterite soil after they have taken this course: They see the regolith differently now.”

Interpretation of Artisanal Gold Workings

Investigating laterite-hosted gold being mined by artisanal gold miners. laterite hosted gold means the primary source is proximal, not necessarily directly below because of the mushroom-dispersal effect of gold in the laterite regolith, but close.

  • Geographical locations, in particular with relation to elevation/topography.

  • Style of gold mining: Laterite or saprolite-hosted? Gravel/alluvial/placer gold? Colluvium-bearing gold?

  • Trace the alluvial gold back upstream, colluvium gold upslope, whereas laterite and saprolite hosted gold workings are proximal.

  • Primary gold proximity and controlling structures can be deduced by investigating historic and active artisanal and small-scale gold workings in the project area.

Aerial view of small-scale gold miners that mine primary, hard rock. their blue tarps on the south and north ends of the image show clustering of gold workings along specific trends, marking possibly fold-nose-related control on gold mineralization.
Laterite hosted gold workings by porknockers in Suriname. gold nuggets are formed at the base of the laterite and the gold miners use pressurized water hoses to create a slurry of laterite and saprolite mud, then sluice the slurry for gold nuggets.
Danae Voormeij in the jungles investigating artisanal gold mining pits, the orange red colours of the water is from acid rock drainage from the sulphide-rich waste rock.

Gold Project Technical Review

Mynah Exploration technical due diligence draws on 25 years of direct field experience across more than 25 countries.

Historical data is compiled, structural controls on gold identified, 3D geological models interpreted and constructed, field site visits are made, gold potential is assessed and knowledge transfer made.

Whether you are a private investor considering entry into a new gold mining district or a company requiring an independent opinion from a Qualified Person (QP) on a gold exploration project, Mynah Exploration delivers technical assessments.

All engagements are strictly confidential.

3D Vein Modelling

3D hand modelled sub parallel orogenic gold bearing quartz veins explicit modelling using Micromine

Understanding the three-dimensional geometry of gold-bearing vein systems is critical for exploration drilling, resource modelling and mine design.

Mynah Exploration is experienced at 3D explicit vein modelling, where veins are manually built up from interpreted drill sections, using core structures, such as alpha angles of foliation and quartz veins, and gold grades from drill core or underground sampling, and mineral alteration.

Turn historical mine maps into three-dimensional structures, discover new veins, and identify plunge directions of ore shoots.

The flythrough video above shows an extensive explicit (hand)-modelled 3D vein system by Mynah Exploration for the historic Venice Mine Complex in Zimbabwe, composed of 7 separate vein systems.

Surface artisanal gold workings are shown in red, illustrating the relationship between artisanal mining activity and the underlying vein architecture.